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Far-infrared optical conductivity gap in superconducting MgB2 films
Robert A Kaindl1, Marc A Carnahan, Joseph Orenstein
1Department of Physics, University of California at Berkeley, and Materials Sciences Division, E. O. Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
Physical Review Letters
|January 22, 2002
Summary
This study investigates the optical conductivity of Magnesium Diboride (MgB2) using terahertz spectroscopy. We observed a superconducting energy gap around 5 meV, indicating complex behavior in this novel material.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Superconductivity
Background:
- Magnesium Diboride (MgB2) is a novel superconductor with potential applications.
- Understanding its superconducting properties, particularly the energy gap, is crucial for further development.
- Previous studies have not fully characterized the optical conductivity near the lowest-energy superconducting gap.
Purpose of the Study:
- To investigate the optical conductivity of MgB2 thin films.
- To determine the frequency-dependent complex conductivity sigma(omega).
- To analyze the superconducting energy gap and its implications for MgB2's behavior.
Main Methods:
- Terahertz time-domain spectroscopy was employed.
- Complex, frequency-dependent conductivity sigma(omega) was measured for thin MgB2 films.
- The optical response was analyzed across the superconducting transition.
Main Results:
- An inductive response in the imaginary part of conductivity confirmed the superconducting condensate.
- A significant depletion of oscillator strength in the real part near 5 meV indicated the opening of the superconducting energy gap.
- The derived gap ratio (2Delta0/k(B)TC ≈ 1.9) is below the weak-coupling BCS theory prediction.
Conclusions:
- The optical conductivity measurements reveal the opening of a superconducting energy gap in MgB2 around 5 meV.
- The observed gap ratio suggests that MgB2 exhibits complex superconducting behavior beyond simple weak-coupling models.
- This study provides critical insights into the fundamental superconducting mechanisms of MgB2.